Method for stabilizing soils and abating active slides

ABSTRACT

Stabilization of soil masses and abatement of active slides are accomplished by applying an aqueous solution, slurry or powder, of a chemical agent to the soil. The chemical agent is selected from ammonium, and mono, di, and trivalent metal salts of carboxylic acids, usually dicarboxylic acids of from two to six carbon atoms; ammonium and mono, di, and trivalent metal fluorides and polyfluorides; ammonium and mono, di, and trivalent metal fluoborates, fluosilicates and fluorophosphates; ammonium and alkali metal salts of phosphoric and polyphosphoric acids; sulfate salts of mono, di, and trivalent metals; cupric chloride; stannic (IV) chloride; and borate salts of metals.

llnited States Arora i atent 1 [75] Inventor:

[73] Assignee:

[22] Filed: May 5, 1971 [21] Appl. No.2 140,624

[52] US. Cl. ..61/36 R [51] Int. Cl ..E01c 11/24, E02d 3/12, E02d 3/14[58] Field of Search ..6l/36 R, 35

[56] References Cited UNITED STATES PATENTS 3,503,215 3/1970 Graf et al...6l/35 3,490,241 l/l970 Kuhn 61/36 R 2,200,710 5/1940 Bent et al....6l/36 R 3,288,040 11/1966 Burrows 61/36 R X 3,075,851 l/l963 Hemwall..6l/36 R Harpal S. Arora, Daly City, Calif.

Edward D. Graf, Daly City, Calif.

[ 11 3,732,698 [4 1 May 15, 1973 Primary Examiner-Stephen J. Novosad Atlorney- Townsend and Townsend 57 ABSTRACT Stabilization of soil massesand abatement of active slides are accomplished by applying an aqueoussolution, slurry or powder, of a chemical agent to the soil. Thechemical agent is selected from ammonium, and mono, di, and trivalentmetal salts of carboxylic acids, usually dicarboxylic acids of from twoto six carbon atoms; ammonium and mono, di, and trivalent metalfluorides and polyfluorides; ammonium and mono, di, and trivalent metalfluoborates, fluosilicates and fluorophosphates; ammonium and alkalimetal salts of phosphoric and polyphosphoric acids; sulfate salts ofmono, di, and trivalent metals; cupric chloride; stannic (1V) chloride;and borate salts of metals.

14 Claims, N0 Drawings METHOD FOR STABILIZING SOILS AND ABATING ACTIVESLIDES This invention relates to the treatment of soils by theapplication to the soil of a chemical agent containing soil stabilizinggroups, and more particularly to new chemical agents for effecting soilstabilization and slide abatement.

In U. S. Pat. No. 3,490,241, a method for stabilizing soils is describedwherein an organic or inorganic salt is formulated in an aqueoussolution and thereafter applied to a soil to be treated. The applicationand distribution of the solution is accomplished by physical diffusionof the ions through the soil so that the soil is stabilized at locationsspaced from as well as at the point of application. Suitablestabilization agents included aqueous solutions of aluminum chloride,aluminum nitrate, ferric chloride, low molecular weight amine-acidsalts, calcium chloride, calcium orthophosphate, and ammonium phosphate.

In U. S. Pat. No. 3,503,215 a method for treating an active soil slideis described wherein the soil stabilizing agents disclosed in U. S. Pat.No. 3,490,241 are directly contacted with at least a portion of the slipsurface of an active slide to prevent further sliding. It was found thatby contacting the slip surface with stabilizing agents the sliding couldbe abated.

Additional stabilization agents have now been discovered for use in theabove-described techniques for stabilization of soils, reduction orelimination of expansiveness or swelling, and abatement of active soilslides. These agents are characterized in that they are water solubleand ionizable. They are further characterized in that they containcations and anions which can interact with the soil colloidal materialsto effect a stabilization thereof. In many cases, these agents are farmore effective in stabilizing soils than those agents heretoforedisclosed in the above-described prior art.

That the agents for use in this invention were effective in soilstabilization was unexpected in view of the unpredictability associatedwith said chemistry. It was further found that many of these same agentsexhibited even greater utility in achieving soil strengthening than thepreviously disclosed agents of the prior art, even though they containedthe same cations.

In particular, the soil stabilizing agents for use in this invention areselected from one of the following classes of compounds:

1. ammonium and mono, di, and trivalent metal salts of carboxylic acids,usually dicarboxylic acids of from two to six carbon atoms. Exemplarysalts include ammonium citrate, potassium citrate, ammonium oxalate,potassium oxalate, sodium citrate, sodium oxalate, ammonium tartrate,ferric oxalate, potassium tartrate, ferric ammonium citrate, sodiumtartrate, ammonium benzoate, potassium formate, barium acetate, aluminumlactate, magnesium formate, potassium succinate, and the like;

2. ammonium and mono, di, and trivalent metal fluorides andpolyfluorides. Exemplary salts are potassium fluoride, ammoniumfluoride, ammonium bifluoride, aluminum fluoride, sodium fluoride, andthe like;

3. ammonium and mono, di, and trivalent metal fluoborates, fluosilicatesand fluorophosphates. Exemplary salts are ammonium fluosilicate,ammonium fluoborate, magnesium fluosilicate, zinc fluosilicate, ammoniumhexafluorophosphate and potassium hexafluorophosphate, and the like;

4. ammonium and alkali metal salts of phosphoric and polyphosphoricacids. Exemplary salts are mono and di-basic ammonium phosphate, monoand di-basic potassium phosphate, mono and dibasic sodium phosphate,potassium tripolyphosphate, sodium ammonium phosphate, sodiumpyrophosphate, and the like;

5. sulfate salts of mono, di, and trivalent metals. Ex emplary salts arealuminum ammonium sulfate, aluminum potassium sulfate, aluminum sulfate,ferric sulfate, ferric aluminum sulfate, chromium potassium sulfate,ammonium ceric sulfate, and cupric sulfate;

6. cupric chloride;

7. stannic (IV) chloride;

8. borate salts of metals. Exemplary compounds are cadmium borate andpotassium borate.

Usually the salts will be water soluble at ambient temperatures (about20 C.) to at least about 0.5 or more weight percent, more usually about1 weight percent. The alkali metal phosphates, polyphosphates and saltsof dicarboxylic acids of from about two to six carbon atoms, e.g.oxalates, citrates and tartrates, are most frequently found to beeffective in the present technique. Also, the alkali metal fluoboratesand fluosilicates very frequently can be used to advantage.

While all of the above-described agents are effective in stabilizing atleast some soils, some are more effective than others. The effectivenessof each agent is dependent upon the particular soil being treated.Though not wishing to be bound by the following theory, it is believedthat both the cations and anions of the soil stabilizing agents of thisinvention are involved in exchange with the soil and/or bonding as byhydrogen bonding. It has been observed that various soils adsorb anionsthat can be subsequently exchanged with other anions to thus exhibit ananion exchange capacity. Other soils are capable of direct anionexchange. Thus, when the agents of this invention are dissolved, boththe anions and cations in solution are free to interact and exchangewith cations and anions naturally occurring on the soil colloids.

To insure maximum ion exchange, and thus maximum soil stabilization, theselected salts should preferably contain ions which do not naturallyoccur in the soil being treated at least in soluble forms. For example,it is known that calcareous soils contain carbonates and bicarbonates.Acidic soils, on the other hand, contain large amounts of solublephosphate and sulfate ions. It has also been observed that chlorides,nitrates, and sulfates are to be found in soils of any pH. Thus, if aphosphate salt such as ammonium phosphate were applied to an acidicsoil, which already has an adequate amount of soluble phosphates,relatively little anion exchange can occur. However, when that sameagent is added to a calcareous soil, which usually don't have solublephosphates present, a much greater increase in soil stabilization isobserved due to the increased anion exchange possibilities.

It appears that the anions of the carboxylic acid salts not onlyinteract and exchange with anions already present in the soil, but tendto increase the solubility of naturally occurring phosphates and otheranions like silicates, in the soil such as the aluminum and ironphosphates. The more phosphate anions in solution,

the more there are available for exchange with other anions in the soil.

It is to be appreciated that the amounts of the salts to be employed aswell as the methods of application of the agents of this invention arein accordance with those set forth in the above-mentioned patents. Theagent can be applied as a solution over the ground to be treated or inthe case of an active slide, applied directly to a slip plane of theslide as by pouring solution into tension cracks and fissures.

Surface application is contemplated as well as subsurface applicationwherein the chemical can be added to holes bored in the ground. In .thecase of active slides, these chemicals are applied as close to the slipplane as possible and are also added in excess near other observed weakplanes so that new slip planes do not develop.

A sufficient amount of the agent will be used to effectuate an increasein soil strength. Generally, it will be desirable to saturate or satisfyat least a substantial portion of the ion exchange and adsorptioncapacity of the soil being treated. As pointed out in copendingapplication Ser. No. 75,749, filed Sept. 25, 1970, the concentration ofthe stabilizing chemicals is not a critical factor for most of thesoils. Small amounts of about 1 percent by weight and less have beenfound to be effective in soil stabilization. Dry powder or concentratedslurries of chemicals when applied at strategic points have beenobserved to distribute themselves by mass flow or diffusion.

The invention is primarily adapted for use with claytype soils or thosewhich become clay-like in physical or chemical properties when moist. Insome cases it is also possible to stabilize fine silts as they also showcation and anion exchange capacities. It will be appreciated that clayas a generic term covers many different types of materials suchasillitic clays, vermiculitic clays and montmorillonitic clays. Further,no two clay containing soils are exactly alike in their chemical makeup.As their compositions differ, so will the types of cations and anionscontained therein. For a particular soil in a given region, one salt maybe more suitable than another. The determination of which salt willafford the greatest soil stabilization can be established by routinelaboratory procedures.

It may well be that no single ionizable salt is best suited. Theadmixture of two or more salts may thus be indicated for a given soil.To this end, it is preferred to initially take small samples of the soilto be treated and apply to them a plurality of the agents of the typedescribed herein. In this way, the optimum chemical or mixture ofchemicals can be used to stabilize the soil. By selection andcombination of several salts, a standard formulation can be provided foreffective treatment of a variety of soil types which may be encounteredin a given geographical region or soil series.

The following examples are presented to illustrate the invention. Foursoils were studied. Various agents in accordance with this inventionwere added to these soils, and the strength of the soils measured after1, 7, and 28 days. Of the four soils, three were slightly basic, and oneslightly acidic. In each run, a sufficient amount of a 2 percent aqueoussolution of a soil stabilizing agent was added to approximately 150grams of soil to bring the soil consistency to near its liquid limit.

EXAMPLE 1 Samples of Atherton soil, an expansive fat clay soil fromAtherton, San Mateo County, Cal., containing 24 percent calciumcarbonate were treated with an aqueous solution or slurry containing thevarious stabilizing agents of this invention, and the strength of thesoil samples determined after 1, 7, and 28 days using a vane sheardevice calibrated in inch ounces. In this and all other examples, thecontrol run comprised distilled water. The results are reported below.

TABLE I ATHERTON SOIL Observed soil strength after AGENT l Day 7 Days 28Days 1. Ammonium Fluoborate 30 32 40 2. Potassium Phosphate Dibasic 3634 56 3. Potassium Citrate 42 44 68 4. Aluminum Potassium Sulfate 38 4440 5. Ferric Sulfate 25 26 26 6. Magnesium Fluosilicate 28 32 4O 7.Sodium Ammonium Phosphate 48 50 52 8. Sodium Citrate 36 44 44 9. SodiumPhosphate Monobasic 38 52 50 IO. Cupric Chloride 36 40 5O 0 Control 1718 18 Aluminum Chloride 16 22 25 Ferric Chloride 19 20 25 AluminumNitrate 22 25 24 From the above, it can readily be seen that, ingeneral, the phosphate and carboxylic acid salts were the most effectivein stabilizing the Atherton soil. This was not unexpected since Athertonsoil is an alkaline soil, low in phosphate ion concentration. It is alsoto be noted that the ammonium fluoborate, aluminum potassium sulfate,and magnesium fluosilicate were likewise effective.

To illustrate that both anion and cation exchange have occurred,attention is directed to the reported results for aluminum potassiumsulfate, ferric sulfate, aluminum chloride and ferric chloride. Thealuminum potassium sulfate was more than percent effective than thealuminum chloride, even after 28 days. The ferric sulfate was about 20percent more effective than the ferric chloride after 1 day.

EXAMPLE 2 In a manner similar to Example 1, an expansive fat clay soilfrom Palmdale, Los Angeles County, Cal., was treated with various soilstabilizing agents; the results are reported below.

TABLE II PALMDALE SOIL Observed soil strength after Again, the phosphateand carboxylic acid salts were most effective for soil stabilization.Also effective was ammonium fluosilicate and potassium fluoride.Ammonium chloride imparted a soil strength of only 4 inch ounces after 7days, whereas the other ammonium salts were three to nine times moreeffective. Similarly, potassium chloride was particularly ineffective,especially in comparison with the citrate and fluoride salts ofpotassium.

EXAMPLE 3 In a manner similar to Examples 1 and 2, soil samples fromVancouver, Washington were obtained, stabilizing agents of thisinvention added thereto, and the results'reported below.

TABLE III VANCOUVER, WASHINGTON QUARANTINE STATION SOIL L Observed soilstrength after AGENT 1 Day 7 Days 28 Days 1. Ammonium Chloride 5 8 8 2.Ammonium Citrate Dibasic 28 48 32 3. Ammonium Fluosilicate 12 12 6 4.Ammonium Fluoborate 6 6 l4 5. Ammonium Oxalate 24 24 24 6. PotassiumChloride 2.5 2.5 5 7. Potassium Phosphate Dibasic 8 8 10 8. PotassiumCitrate 12 18 18 9. Potassium Fluoride 4 4 4 10. Ferric Oxalate 64 80 88l 1. Magnesium Fluosilicate 40 48 48 12. Sodium Tripolyphosphate 40 5668 13. Sodium Ammonium Phosphate 32 36 48 14. Sodium Citrate 1O 16 2015. Zinc Pluosilicate 6 6 6 0 Control 15 15 Ferric Chloride 2 2 2 Again,the dicarboxylic acid and phosphate salts were generally effective. Thesoil being slightly acidic, it was not surprising to find that someagents, effective with basic soils, were relatively ineffective herein.

EXAMPLE 4 Following the procedures of the above examples, a Danvillesoil was obtained and various samples of the soil mixed with variousagents according to this invention, the results recorded below. TheDanville soil is an expansive clay soil from Danville, Cal., and has acalcium carbonate content of approximately 18 percent.

TABLE IV DANVILLE SOIL observed soil strength after As in the previousexamples, the dicarboxylic acid salts were uniformly effective instabilizing the soil, as were the phosphates. Also reasonably effectivewere potassium fluoride, and zinc fluosilicate.

From the above experiments it is apparent that no one single agent isbest suited for any particular soil. In some cases, a fluoride salt suchas potassium fluoride may be particularly effective such as with aDanville type soil. In other cases it may be particularly ineffectivesuch as with a soil from Vancouver, Washington. Thus, the need fortesting samples ofa given soil which may include a chemical analysis ofits pore water before a treatment program is begun is evident. It isalso apparent that certain phosphate salts and most of the dicarboxylicacid salts are effective for almost all the types of soil tested.

What is claimed is:

1. In the method for treating soil to stabilize it, to reduce oreliminate expansiveness, or to abate active sliding by distributing aneffective amount of water soluble ionizable chemical to the soilincluding the slip plane where active sliding is to be abated, saidchemical providing soil strengthening ions when ionized in the soil ofthe type that stabilizes the lattice of the soil particles by mechanismsincluding ion exchange with exchangeable ions naturally occurring in thesoil particle lattice, the ions provided by said chemical being in anamount sufficient to stabilize the soil being treated, the distributionof said ions including diffusion through the soil by ionic migration tostabilize the area of said migration by ion exchange, the improvementwherein said chemical composition includes at least one member selectedfrom the group consisting of ammonium and mono, di and trivalent metalsalts of carboxylic acids; ammonium and mono, di, and trivalent metalfluorides and polyfluorides; ammonium and mono, di, and trivalent metalfluoborates, fluosilicates and fluorophates; ammonium and alkali metalsalts of polyphosphoric acids; alkali metal salts of phosphoric acid;sulfate salts of mono, di, and trivalent metals; cupric chloride;stannic (IV) chloride; and borate salts of metals.

2. The improved method according to claim 1 wherein said chemicalcomposition includes a metal salt of a carboxylic acid which is anoxalate, citrate, tartrate, benzoate, formate, acetate, lactate orsuccinate.

3. The improved method according to claim 1 wherein said chemicalcomposition includes a metal fluoride, metal fluoborate or metalfluosilicate.

4. The improved method according to claim 1 wherein said chemicalcomposition includes an alkali metal phosphate or polyphosphate.

5. The improved method according to claim 4 wherein said chemicalcomposition includes an alkali metal polyphosphate.

6. The improved method according to claim 5 wherein said alkali metalpolyphosphate is potassium tripolyphosphate.

7. The improved method according to claim 4 wherein said chemicalcomposition includes tetrapotassium pyrophosphate.

8. The improved method according to claim 1 wherein at least about oneweight percent of said chemical composition is applied to the soil.

9. The improved method according to claim 1 wherein said chemicalcomposition includes a metal sulfate salt.

10. The improved method according to claim 1 wherein said chemicalcomposition includes cupric chloride.

11. The improved method according to claim 1 wherein said chemicalcomposition includes stannic (IV) chloride.

12. The improved method according to claim 1 wherein said chemicalcomposition includes metal borate.

and fluorophosphates; ammonium and alkali metal salts of polyphosphoricacids; alkali metals salts of phosphoric acid; sulfate salts of mono,di, and trivalent metals; cupric chloride; stannic (IV) chloride; andborate salts of metals.

14. The improved method in accordance with claim 13 wherein the soilbeing treated is an expansive, fat

clay soil.

2. The improved method according to claim 1 wherein said chemicalcomposition includes a metal salt of a carboxylic acid which is anoxalate, citrate, tartrate, benzoate, formate, acetate, lactate orsuccinate.
 3. The improved method according to claim 1 wherein saidchemical composition includes a metal fluoride, metal fluoborate ormetal fluosilicate.
 4. The improved method according to claim 1 whereinsaid chemical composition includes an alkali metal phosphate orpolyphosphate.
 5. The improved method according to claim 4 wherein saidchemical composition includes an alkali metal polyphosphate.
 6. Theimproved method according to claim 5 wherein said alkali metalpolyphosphate is potassium tripolyphosphate.
 7. The improved methodaccording to claim 4 wherein said chemical composition includestetrapotassium pyrophosphate.
 8. The improved method according to claim1 wherein at least about one weight percent of said chemical compositionis applied to the soil.
 9. The improved method according to claim 1wherein said chemical composition includes a metal sulfate salt.
 10. Theimproved method according to claim 1 wherein said chemical compositionincludes cupric chloride.
 11. The improved method according to claim 1wherein said chemical composition includes stannic (IV) chloride. 12.The improved method according to claim 1 wherein said chemicalcomposition includes metal borate.
 13. In the method for treating anactive soil slide by treating at least a portion of the established slipplane or slip surface with a sufficient amount of a chemical stabilizingagent to halt sliding along said slip plane or surface, the improvementwherein said chemical stabilizing agent is selected from the groupconsisting of ammonium and mono, di, and trivalent metal salts ofcarboxylic acids; ammonium and mono, di, and trivalent metal fluoridesand polyfluorides; ammonium and mono, di, and trivalent metalfluoborates, fluosilicates and fluorophosphates; ammonium and alkalimetal salts of polyphosphoric acids; alkali metals salts of phosphoricacid; sulfate salts of mono, di, and trivalent metals; cupric chloride;stannic (IV) chloride; and borate salts of metals.
 14. The improvedmethod in accordance with claim 13 wherein the soil being treated is anexpansive, fat clay soil.